The present invention generally relates to apparatus for torque transfer between a male shaft and a female hub, particularly to apparatus providing a keyed connection between a male shaft slideable within a female hub, and specifically to apparatus for locking a key between a male shaft slideable within a female hub.
Rotational control apparatus are often face mounted between an input unit and an output unit. As an example, clutch-brakes are typically ANSI and NEMA C face mounted between an electric motor and a gearbox. The method of torque transfer in these designs is a keyed shaft between the male motor shaft and the female clutch-brake hub and also between the male clutch-brake shaft and the female gearbox hub. Because of the cycling nature of the clutch-brake, the torque applied to each of these shaft/hub connections reverses. This reversing load has the tendency to result in an impact between the key and the keyways. Over time, these impacts begin to enlarge the keyways. The enlarged keyways cause greater impacts which accelerates the damage. Eventually the keys tend to roll the material around the keyway and cause a catastrophic failure.
Typical keyed shafts use set screws threaded in the hub and engaging the key to lock the key into the keyway. As an example, the female hub of clutch-brakes often have a set screw located over the keyway in the hub for locking the key into the keyway of the motor shaft. It can then be appreciated that access to this set screw must be provided such as via a pipe port in the side of the clutch-brake. Locking the key between the bottom of the keyway in the shaft and the bottom of the set screw (which effectively becomes the bottom of the keyway in the hub carried by the shaft) has proven to be very effective in eliminating any tendency for the key to roll and damage the keyways in keyed connections.
Gearboxes are made to ANSI and NEMA standards which dictate the hole size, key size, and depth of bore. Because of this, the manufacturers of gearboxes have not made accommodations to lock the keys in place. Thus, the keyed connection between the male shaft of the clutch-brake and the female hub of the gearbox encounter problems of keyway damage due to reverse loading.
Various solutions have been previously utilized by manufacturers of clutch-brakes to lock the male shaft of the clutch-brake to the female hub of the gearbox for transferring torque therebetween. However, such solutions encounter various drawbacks including but not limited to complexity, strength, and lack of positive engagement.
Thus, a need continues to exist to provide a manner of providing positive torque transfer from a male shaft to a female hub slideably receiving the male shaft. In preferred aspects of the present invention, a need continues to exist to provide a manner to lock the key in a keyway when locking accommodations are not available in the female hub.